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Cities around the world pursue urban renewal under the banner of resilience and diversity. The idea is simple: if neighborhoods include socially and economically diverse residents, it will lead to stronger social cohesion, greater trust, and mutual support among the community. One common approach is to mix residents from different income groups within the same neighborhood.

In Rotterdam, this idea has been formalized through a policy that targets the mix of housing values in what the city calls "balanced neighborhoods." By adjusting the proportion of low-, middle-, and high-value housing in each area, the goal is to create socially cohesive and resilient communities.

But a new study by the Complexity Science Hub (CSH) and Delft University of Technology, published in , raises serious doubts about whether this approach—also applied in a similar way in cities like Berlin and New York—delivers on its promise.

No boost to trust

The researchers used detailed housing value data and survey responses from residents across Rotterdam to evaluate how the city's policy affects social cohesion—that is, how connected, trusting, and supportive people feel toward each other in a community.

They tested over 3,000 possible combinations of housing values that qualify as "balanced" under Rotterdam's official guidelines. "There was little evidence that most housing value mixes led to stronger community ties, and in the few cases where a link existed, the effect was negative," says CSH researcher Guillermo Prieto-Viertel.

In fact, only 2.1% of balance configurations were associated with changes in neighborly support—and even then, they showed less support. "In other words: most of what the city calls 'balance' has little to no link to how much neighbors trust or help one another," explains Prieto-Viertel.

Focus on people, not property values

"Our study shows how policies intended to promote inclusion can enable gentrification and displacement, and how ambiguous measures can be used to justify displacing low-income communities while claiming to promote inclusion. In an era of rising housing inequality, this matters more than ever," says Prieto-Viertel.

Rotterdam reflects a broader international trend where cities adopt social mix strategies around the world. Cities like Auckland, Singapore, London, and Toronto also promote "social mix" through housing or real estate strategies.

What should be done?

"Vague or overly technical indicators should not guide decisions that affect people's lives. Rotterdam's example shows that the definition of 'balance' is so vague it can be used to label both wealthy and poor areas as balanced," explains Prieto-Viertel. "This can misguide renewal efforts and lead to the displacement of communities that don't actually lack cohesion."

Instead, urban strategies should be grounded in direct measurements of social outcomes—such as levels of trust, mutual aid, and community engagement—and developed with input from the residents they aim to serve. For example, regularly surveying communities about how connected and supported they feel can provide far more actionable insights than property values alone.

How cities survive in crises

Resilience is increasingly used to describe a city's ability to cope with shocks—whether pandemics, heat waves, or social unrest. "But this resilience isn't just about infrastructure or emergency plans, it's about whether people help each other in times of crisis," says Prieto-Viertel.

"That depends on social cohesion and trust, which are often damaged when redevelopment displaces long-standing communities. When policies prioritize housing values over human relationships, they can inadvertently weaken the community bonds that make cities truly resilient."

He cites one example: In the U.S., the HOPE VI program displaced thousands of public housing residents in the name of "mixing" but broke apart long-standing social networks.

"If we shift toward real estate metrics to define inclusion, we risk weakening the very cohesion we want to promote," warns Prieto-Viertel. "Instead, we should measure what actually matters—how people relate to and support one another."